The present invention relates to a semiconductor memory device, and more particularly to a pull-down circuit for wide voltage operation of static random access memory (SRAM) devices.
According to the rapid development of semiconductor memory devices, demand for such semiconductor memory devices has been increased in various technical fields so that the devices can be used for a variety of products.
However, the specifications required for individual products are infinitely various. In particular, the supply voltage source has the variety depending on the product characteristic. For individual products, proper semiconductor memory devices are required which can operate to meet the supply voltage sources used for individual products, respectively.
Generally, 5 V operating voltage is used in SRAMs. In case of portable appliances, however, 3 V operating voltage is required. Where a semiconductor memory device has no pull-down circuit, a low read speed is obtained even though the voltage difference between data lines, namely, the sensing voltage is high. This makes it impossible to use the semiconductor memory device. The low read speed results from a low sensibility of a MOS transistor of the semiconductor memory device.
On the other hand, 5 V-operable products equipped with pull-down circuits can perform a normal operation. However, 3 V-operable products equipped with pull-down circuits can perform a read operation for reading a sensing voltage because the sensing voltage is very low. As a result, these products can not be used with 3 V operating voltage.